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:I studied ants at one point. I found that the red ants ate more than the black ants. I could never determine why for sure, but I hypothesized that my experiment had more red ants than black ants. ←[[User:Baseball Bugs|Baseball Bugs]] <sup>''[[User talk:Baseball Bugs|What's up, Doc?]]''</sup> [[Special:Contributions/Baseball_Bugs|carrots]]→ 16:03, 9 August 2021 (UTC) |
:I studied ants at one point. I found that the red ants ate more than the black ants. I could never determine why for sure, but I hypothesized that my experiment had more red ants than black ants. ←[[User:Baseball Bugs|Baseball Bugs]] <sup>''[[User talk:Baseball Bugs|What's up, Doc?]]''</sup> [[Special:Contributions/Baseball_Bugs|carrots]]→ 16:03, 9 August 2021 (UTC) |
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== Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination — Kentucky, May–June 2021 == |
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Can someone please help me to understand this article in layman's terms?[https://www.cdc.gov/mmwr/volumes/70/wr/mm7032e1.htm?s_cid=mm7032e1_w&fbclid=IwAR1MBWT8anGPg4rpvV4mHwAFiPS6ufaBJV_pICNJzEK2yD4y05QoDN7_BdU] It says that unvaccinated COVID survivors are twice as likely to get reinfected than COVID survivors who get vaccinated. But what does "twice as likely" actually mean? If, for example, the reinfection rate of the former is 93% and 96% for the latter, isn't that "twice as likely"? Is it possible to sus out the actual reinfection rates from this article? [[User:A Quest For Knowledge|A Quest For Knowledge]] ([[User talk:A Quest For Knowledge|talk]]) 20:04, 9 August 2021 (UTC) |
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August 3
Plants - berry and juices questions.
Strawberries, raspberries, and blackberries roughly have the same lifespan, they decay quickly to room temperature. Blueberries spoil/decay 5x slower, so they can last 5x longer. Why is that? I heard the answer has something to do with respiration. All of them must be kept at 33 F - 35 F or 1-2 C. Problem is if it goes to 0 C, ice forms, but the issue isn't when ice forms, but when ice melts, then expansion damages the fruit.
Then, what about juices? Why are some juices can last much longer, and in room temperature, than other juices? By looking at expiration dates, cherry juice seems to last a year from shelf life. And apple, grape, and pear juices tends to be mixed together, but not with shorter-lifespan juices like strawberry. So, nobody sells a "blueberry-strawberry" juice mix, certainly not at room temperature, not because of the blueberry, but because of the strawberry. I've never seen a cranberry-strawberry, but I do see cranberry-raspberry, which is puzzling to me, because raspberry juice has the same shelf life as strawberry juice? Does cranberry juice actually have an effect that increases the lifespan of raspberry juice, for example? That it would not otherwise do with strawberry juice? Raspberry and blackberry juice can be mixed together because of their same-lifespan / shelf life.
So what is it in strawberry juice that makes it the shortest shelf life, that has to be refrigerated the most? Thanks. 67.165.185.178 (talk) 03:42, 3 August 2021 (UTC).
- Juices are covered by a rather unique Juice HACCP program. Typically they are pasteurized, so I'll bet that the shelf life of strawberry juice is not because it is any more likely to be affected by microbial growth, but by physical changes. I'm guessing it turns an ugly color very quickly. Abductive (reasoning) 08:07, 3 August 2021 (UTC)
- Another thing that can go wrong is that a solid deposit comes out of the juice and onto the container, which looks ugly. Graeme Bartlett (talk) 22:58, 3 August 2021 (UTC)
- I rather suspect that strawberry juice is less acidic than blueberry, raspberry, etc, which could account for a shorter shelf-life. DuncanHill (talk) 20:02, 4 August 2021 (UTC)
- Another thing that can go wrong is that a solid deposit comes out of the juice and onto the container, which looks ugly. Graeme Bartlett (talk) 22:58, 3 August 2021 (UTC)
As a related question, what causes certain juices, required to be refrigerated at grocery stores - orange juice, strawberry juice, whereas other juices can be sold at room temperature. 67.165.185.178 (talk) 23:56, 4 August 2021 (UTC).
- Since no one has answered, I'll volunteer that I'm guessing this depends a lot on how the juice was processed and packaged, as well as other factors like local regulations, norms, preferences etc. You can definitely buy a lot orange juice that is sold at room temperature in NZ. Most of this is reconstituted from concentrate but I think some are not. These are normally sold either in plastic bottles or Tetra Pak and have a best before date of months from manufacturing date. Strawberry not so much although I'm not certain this is because it's not possible but could be instead an issue of cost etc. Although this source mentions [1] the high-acid factor as the reason UHT is not normally required so DuncanHill might be right on strawberry juice. BTW our article mentions that Cold-pressed juices tend to have a very short shelf life. Also I'm fairly sure apple+strawberry or pretty much any apple whatever mix exists unless it tastes so bad no one wants it (or it's too expensive for the potential market or simply no one has bothered) e.g. [2] [3]. Note the last one may say "Strawberry and Kiwifruit" but if you look carefully it says "with apple base" which was a big part of my point. Surprisingly our article doesn't seem to deal with this but apple juice is a very common "base" for fruit juices. It's cheap with a fairly neutral sweet flavour. So depending on local regulations, it enables manufacturers to claim their produce is 100% juice (or whatever) and has no added sugar while producing a sweet cheap to make product with a small amount of strawberry or whatever else they promote and many dietitians etc are doubtful is much better than most soft drinks. See e.g. [4]. Nil Einne (talk) 17:15, 9 August 2021 (UTC)
Electron flow
Do electrons flow differently in a wire than in a circuit? Here's what I gathered.
In a wire: both electrons and protons travel from high voltage to low voltage.
In a circuit: electrons will flow from a point of more negative voltage to that of a more positive voltage. Electricity travels from high negative charge (lots of free electrons) to low negative charge or even positive charge (missing electrons). High voltage means more difference in charge, low voltage means less difference in charge.
I presume these aren't contradicting? 67.165.185.178 (talk) 05:45, 3 August 2021 (UTC).
- Electricity goes from the positive side to the negative side. This is just a definition, made up before electrons were discovered. In wires (and most circuits are made of wires) the electrons move in the opposite direction. The protons don't move. Electrons have a negative charge and a flow of negative charge in one direction gives the same current as a flow of positive charge in the opposite direction. But an electric current isn't always a flow of free electrons. When we send electric current through sea water, we get positively charged sodium ions moving from positive to negative and negatively charged chloride ions moving from negative to positive, both coming from the dissolved salt. PiusImpavidus (talk) 08:15, 3 August 2021 (UTC)
- So to give direct answers:
- "In a wire: both electrons and protons travel from high voltage to low voltage." Incorrect. The electrons travel from negative voltage to positive voltage, the protons don't travel.
- "In a circuit: electrons will flow from a point of more negative voltage to that of a more positive voltage." Correct, except that the electric current isn't always carried by electrons – but in a wire, or a circuit made of wires, it is.
- "Electricity travels from high negative charge (lots of free electrons) to low negative charge or even positive charge (missing electrons)." Incorrect, it's the opposite. Electricity goes from positive to negative, although the electrons go from negative to positive. And the current goes from positive potential to negative potential (voltage between two points in a circuit is the difference in potential between those points), not from positive to negative charge, although with non-zero capacitance those are correlated.
- "High voltage means more difference in charge, low voltage means less difference in charge." Almost. In real circuits, capacitance is never zero and the voltage is proportional to charge divided by capacitance. In ideal circuits (and many real-life electric components are close enough to ideal), capacitance is taken as zero (except where, by design, it's not), so there is no charge, but still voltage. PiusImpavidus (talk) 09:04, 3 August 2021 (UTC)
- I'm curious where you listed electricity as the opposite direction of electrons. So can we say electricity travels from high voltage to low voltage? (But not electrons). I should ping @Thinking of England:. 67.165.185.178 (talk) 19:01, 3 August 2021 (UTC).
- The direction of current is opposite to the flow of electrons. I think PiusImpavidus explained it correctly. Graeme Bartlett (talk) 22:55, 3 August 2021 (UTC)
- Isn't that what current is, the flow of electrons? Okay, so that's 3 questions: the flow of electrons, the flow of electricity, and the flow of current. -_- 67.165.185.178 (talk) 23:18, 3 August 2021 (UTC).
- No. The most common form of electric current you may be aware of is the flow of electrons through a conductor, and by arbitrary convention we have defined the direction of that electric current to be opposite that of the direction of the flow of electrons. But there are also examples of flow of positive charge carriers (as has been mentioned by other editors here), and those cases also represent an electric current, and by arbitrary convention we have defined the direction of that electric current to be the same as the direction of the flow of those positive charge carriers. -- ToE 23:57, 3 August 2021 (UTC)
- Electric current is the flow of electric charge. When positively charged particles move from A to B, there's a current from A to B. When negatively charged particles flow from A to B, there's a current from B to A. It's just that we had already written down all the laws of electromagnetism (the Maxwell equations) before finding out that the main carrier of electric current in daily life happens to be a negatively charged particle. But that doesn't matter, other than being slightly confusing to people new to the subject. Most electrical phenomena other than in vacuum tubes and semiconductors can be fully understood without getting involved in the concept of electrons. PiusImpavidus (talk) 09:05, 4 August 2021 (UTC)
- Isn't that what current is, the flow of electrons? Okay, so that's 3 questions: the flow of electrons, the flow of electricity, and the flow of current. -_- 67.165.185.178 (talk) 23:18, 3 August 2021 (UTC).
- The direction of current is opposite to the flow of electrons. I think PiusImpavidus explained it correctly. Graeme Bartlett (talk) 22:55, 3 August 2021 (UTC)
- I'm curious where you listed electricity as the opposite direction of electrons. So can we say electricity travels from high voltage to low voltage? (But not electrons). I should ping @Thinking of England:. 67.165.185.178 (talk) 19:01, 3 August 2021 (UTC).
- You rang? (I don't know what you expect from me, but perhaps I can rephrase some of the statements already made.)
- The net direction of flow of a particular type of charge carrier in a particular system at a particular moment is a well defined physical property. If 6.24×1018 electrons per second are flowing through a conductor from point A to point B, this direction of electron flow is true, independent of any convention. But by convention, we measure the direction of "electrical current" as being in the same direction as the net motion of positive charge carriers and the opposite direction as the net motion of negative charge carriers. And when we say that 1 amp of "electricity flows" from point B to point A (in the example above), we mean that the direction of current, as we define it by convention, is from point B to point A -- even though in that example the direction of net charge carrier motion is opposite. That does not mean there are some separate physical particles of a substance called "electricity" which are flowing opposite those electrons. We simply define the "flow of electricity" by that convention.
- Quoting from Electric current§Conventions:
- The direction of conventional current is arbitrarily defined as the direction in which positive charges flow. Negatively charged carriers, such as the electrons (the charge carriers in metal wires and many other electronic circuit components), therefore flow in the opposite direction of conventional current flow in an electrical circuit.
- Does that help?
- As far as flow from high voltage to low voltage, I'd rather not use those terms, as High voltage has a specific meaning. (-10,000 VDC above ground is high voltage, whereas +5 VDC is not.) So speak instead of electricity traveling from more positive voltage to more negative voltage (or to less positive voltage if you wish), and electrons traveling from more negative voltage to more positive voltage. -- ToE 23:49, 3 August 2021 (UTC)
- Okay, your last sentence hit the nail, electricity travels from more positive voltage to more negative voltage, electrons travel from more negative to more positive voltage. Which 1 does current go with? 67.165.185.178 (talk) 01:19, 4 August 2021 (UTC).
- Electricity is a bunch of phenomena in electromagnetism. When we say that electricity flows somewhere, we mean that there is an electric current or a displacement current (a current not consisting of moving charged particles, but of a changing electric field). So the flow of electricity is loosely speaking the same thing as the electric current and it goes from positive to negative. Usually. PiusImpavidus (talk) 09:05, 4 August 2021 (UTC)
- Okay, your last sentence hit the nail, electricity travels from more positive voltage to more negative voltage, electrons travel from more negative to more positive voltage. Which 1 does current go with? 67.165.185.178 (talk) 01:19, 4 August 2021 (UTC).
- One note, is that electricity, even in solid conductors, can be the flow of positive charge. See Electron hole and P-type semiconductor. --Jayron32 14:44, 3 August 2021 (UTC)
- There are also solid ion conductors, eg for lithium or sodium, but they are special materials and not metals. The main electric flow in a metal like wire is carried by electrons. Electric flow will also be accompanied by a magnetic field. Graeme Bartlett (talk) 22:55, 3 August 2021 (UTC)
- "Electricity goes from positive to negative" - well, yes and no. Sometimes electrical current can be thought of as conventional current (positive to negative) or electron current (negative to positive). There are electricity and electronics text books that are available in both versions.
- If you are doing simple electrical circuit analysis you can sometimes pick either conventional current or electron flow. But if you want to understand how vacuum tubes, cathode ray tubes, diodes, transistors, etc function, you have to get real with the physics. There is no abstract magical "electricity goes" that is separate from how electron flow happens.
- Conventional current works in limited circumstances. Like how the "planets circling a star" model of electrons in atoms works in limited circumstances. It's not physically real, but sometimes you can fudge the math to make it give correct answers.
- Conventional current is a historical error. Benjamin Franklin didn't know that electrons existed, and he decided to think of electricity as a flow of positive charges. 85.76.69.130 (talk) 15:44, 4 August 2021 (UTC)
When this something travels from high negative charge (lots of free electrons) to low negative charge or even positive charge (missing electrons), how that be by definition and not observation? Electricity, electrons, and current? How can 1 be defined to the opposite direction of the other? 67.165.185.178 (talk) 19:02, 5 August 2021 (UTC).
- There appears to be a thing called electric charge. It appears to be quite real. For example, when we rub some fur against a piece of amber (the Greek word for which is ἤλεκτρον – elektron), the fur and amber get some property that causes them to attract each other, but two pieces of amber treated this way have a tendency to repel each other, and so do separate hairs of the fur. This property is called electric charge. Some further study reveals that electrically charged objects fall in two categories, such that two objects from the same category repel each other, whilst two objects from different categories attract each other and, when combined, neutralise the charge. The charges can be labelled as positive and negative, and we arbitrarily chose to call the charge in the fur positive and that on the amber negative.
- As observed, opposite charges can neutralise each other and the objects don't even have to be in direct contact, as electric charge can apparently flow through uncharged, conducting objects, like metal rods. So we have such a thing as a flow of electric charge, also known as electric current or colloquially a flow of electricity (but I don't like that phrase), which runs from positive to negative. That makes sense. If there's a positive amount of something in one reservoir and a negative amount in a different reservoir and we connect them to neutralise, the flow of this something must be from positive to negative. And it appears that we can even make such an electric current without first generating measurable separate charges; we can make a setup to separate charges on demand to create a current as soon as the circuit is closed. All of that is classical electromagnetism. Note that I haven't discussed particles yet.
- Now let's add some modern physics. And I really wish people wouldn't mention electrons in books on electromagnetism until they reach the chapter on the photoelectric effect. (OK, you're free to mention electrons when talking about electrochemistry.) So now we introduce the charge carrier. Charge isn't some abstract property of matter that can flow around in so-called conductors; it's a property of some invisible particles that can flow around in so-called conductors. And it appears that the most common charge carrier in daily life electrical circuits is a negatively charged particle, which is appropriately called an electron. Remember that amber got a negative charge? But if a charge carrier, moving to provide an electrical current, has negative charge, it must move in the opposite direction to the flow of positive charge, and therefore to the electrical current.
- BTW, the current most important to humans in daily life is the current running through our nerve cells. This current uses positively charged sodium and potassium ions in a watery solution as charge carriers. PiusImpavidus (talk) 14:56, 6 August 2021 (UTC)
- That's an excellent description. Just to expand a bit on one thing you noted on "classical electromagnetism". It's a shame, really, that we only deal in two domains of understanding of electrodynamics: "classical" and "quantum". Really, there's three domains: there's the classical-classical domain of things like Ohm's law and Coulomb's law and the like, where the laws governing electrodynamics are all governed by nice, easy algebraic equations with a small number of variables. That pretty much covers everything that was discovered prior to James Clerk Maxwell and Oliver Heaviside, and usually covers the sort of electric theory that is enough for practical understanding of most electrical devices, enough for an electrician to wire a house or for a person to do simple repairs on their own electrical devices, etc. Once we get to the Maxwell's equations, we suddenly get VERY complicated VERY fast, but we still live in a "pre-quantum" world. That's because Maxwell and his equations show that electricity, magnetism, and light are ALL manifestations of the same phenomenon, known as electromagnetism, and you can't really properly describe one in isolation. Ohm's law needs basic algebra to solve, something like Gauss's law (one of the four Maxwell equations) needs multidimensional calculus. Then there's the third domain of understanding, that of quantum electrodynamics, or QED, and now we're getting into Richard Feynman's path integrals and the like. --Jayron32 16:29, 6 August 2021 (UTC)
- Okay, I think my question is, what's the difference between conventional current and electron-current? 67.165.185.178 (talk) 19:41, 6 August 2021 (UTC).
- I'm not sure I follow the question. Electric current is the net flow of electric charge in the same way that water current is the net flow of water molecules. Just as you don't actually need to track the motion of individual water molecules to be able to understand how water flows through a pipe, you don't actually need to track how individual charge carriers are flowing in a wire to understand electric current works. At the level of things like Ohm's law, you don't even need to consider such things. You might want to check out some of the electricity videos at the YouTube channel "Science Asylum". Nick Lucid, the presenter, does a very good job and the graphics are top notch. Here is his electricity and magnetism playlist. --Jayron32 23:47, 8 August 2021 (UTC)
- Then why is conventional current in the opposite direction of electron-current? 67.165.185.178 (talk) 01:12, 9 August 2021 (UTC).
- Current moves in the positive direction. Electrons are negative. The sign conventions are necessary to make sure math works out. It's arbitrary WHICH sign conventions are used, and unfortunately, 250 years ago, Benjamin Franklin picked wrong. So now we're stuck with the confusing situation that charge carriers have the opposite sign as the electric current. If you get that time machine built, and talk some sense into him, you can make life much simpler for physics students for the next 250 years. If not, it's just another thing you need to remember. --Jayron32 11:55, 9 August 2021 (UTC)
- I don't think my question was ever about the sign of electrons, but the direction. When electrons flows from (lots of free electrons) to low (missing electrons), but electricity flows from missing electrons, to lots of free electrons, I see that as an observation, not a definition. In my mind, electricity is still the flow of electrons, but they (electricity and electrons) go in opposite directions of each other. 67.165.185.178 (talk) 12:11, 9 August 2021 (UTC).
- Current moves in the positive direction. Electrons are negative. The sign conventions are necessary to make sure math works out. It's arbitrary WHICH sign conventions are used, and unfortunately, 250 years ago, Benjamin Franklin picked wrong. So now we're stuck with the confusing situation that charge carriers have the opposite sign as the electric current. If you get that time machine built, and talk some sense into him, you can make life much simpler for physics students for the next 250 years. If not, it's just another thing you need to remember. --Jayron32 11:55, 9 August 2021 (UTC)
- Then why is conventional current in the opposite direction of electron-current? 67.165.185.178 (talk) 01:12, 9 August 2021 (UTC).
- I'm not sure I follow the question. Electric current is the net flow of electric charge in the same way that water current is the net flow of water molecules. Just as you don't actually need to track the motion of individual water molecules to be able to understand how water flows through a pipe, you don't actually need to track how individual charge carriers are flowing in a wire to understand electric current works. At the level of things like Ohm's law, you don't even need to consider such things. You might want to check out some of the electricity videos at the YouTube channel "Science Asylum". Nick Lucid, the presenter, does a very good job and the graphics are top notch. Here is his electricity and magnetism playlist. --Jayron32 23:47, 8 August 2021 (UTC)
- Okay, I think my question is, what's the difference between conventional current and electron-current? 67.165.185.178 (talk) 19:41, 6 August 2021 (UTC).
CNN report on breakthru covid infections
[5] Does this story say anything meaningful? It got a fair amount of attention. It says less than 1% of vaccinated people have experienced breakthrough Covid infections, but doesn't give a comparison number for non-vaccinated people. Per [6] the current infection rate in California is 16.4 per 100K, which is far below 1%, and actually suspiciously low (can it possibly be right)? I see all kinds of numbers in the news, that are useless as far as I can tell. They are trying to imply things about without giving enough info to actually compute this important ratio.
ObDisclaimer: I'm not looking for medical advice. I'm vaccinated but know someone who is not, who is hassling about it. Thanks. 2601:648:8202:350:0:0:0:2B99 (talk) 06:53, 3 August 2021 (UTC)
- So, this 1% is a sort of prevalence figure? Abductive (reasoning) 08:12, 3 August 2021 (UTC)
- I can't tell. There is no data to show where that number came from. There is some stuff on statnews.com that might be more informative and that I'll try to look at when I can, but it is late here now. If the 16.1/100k figure is the number of
active infectionsnew infections per day right now,and the average one lasts 10 days,then extrapolating over the ~ 500 day pandemic would mean about 8% of the population was infected at one time or another. I guess I can believe that. 2601:648:8202:350:0:0:0:2B99 (talk) 08:32, 3 August 2021 (UTC) (Edited: fix words to fit math).
- I can't tell. There is no data to show where that number came from. There is some stuff on statnews.com that might be more informative and that I'll try to look at when I can, but it is late here now. If the 16.1/100k figure is the number of
- Somewhat more worrying in terms of breakthrough infections is this recent paper on the CDC website."Outbreak of SARS-CoV-2 Infections...". doi:10.15585/mmwr.mm7031e2.
{{cite journal}}
: Cite journal requires|journal=
(help). It suggests that the Delta variant can cause infection even in those who were fully vaccinated. Mike Turnbull (talk) 11:24, 3 August 2021 (UTC)- When the vaccines first came available, I don't recall anyone claiming their vaccine was 100 percent effective against catching the virus. ←Baseball Bugs What's up, Doc? carrots→ 21:33, 3 August 2021 (UTC)
- Somewhat more worrying in terms of breakthrough infections is this recent paper on the CDC website."Outbreak of SARS-CoV-2 Infections...". doi:10.15585/mmwr.mm7031e2.
- In terms of a reference for a Wikipedia article, per WP:MEDRS, CNN is not a qualified source to use for adding such information. If the CNN article cites their sources, I would go to those to learn more. --Jayron32 14:42, 3 August 2021 (UTC)
- This article from the Seattle Times gives the source of the study as the Kaiser Family Foundation - the KFF press release is here and the data summary is here. Alansplodge (talk) 17:34, 3 August 2021 (UTC)
August 4
If we take all water in the atmosphere and collect them together it'll be equall to how many percent of the water on the earth?
If we take all water of the atmosphere (~0.001%) and collect them together, then it'll be equal to how many percent of the water on the earth? Is there any rough information / estimation about it? --ThePupil (talk) 01:09, 4 August 2021 (UTC)
- Actually, sources debunking Creationism may already have done this, as they've done calculations about the thermodynamics of condensing that much water vapor to liquid all at once. Spoiler alert: the amount of heat released by that much condensation would be a lot, as in all life gets cooked alive and dies a lot. I think it is talked about here https://www.youtube.com/watch?v=vWZtbZGtiGA and in this paper https://www.tandfonline.com/doi/abs/10.5408/0022-1368-31.2.134 --OuroborosCobra (talk) 01:19, 4 August 2021 (UTC)
According to Wikipedia, the atmosphere of Earth has a mass of 5.15×1018 kg and contains 0.4% water vapor on average. So there's just over 2×1018 kg of water vapor. 1 g of liquid water has a volume of 1 cm³, so 1 kg has a volume of 1 L, and so 2×1018 kg has a volume of 2×1018 L, which is 2,000,000 km³. Again according to Wikipedia, The total volume of water on Earth is estimated at 1,386,000,000 km³. So the water in the atmosphere is 2/1,386 or about 0.14% of all the water. --184.144.99.72 (talk) 02:24, 4 August 2021 (UTC)
- According to the given data, there are 194040000 km of water in the atmosphare, right? Does it go together with Wisconsin university's statement that the Earth’s atmosphere contains 37.5 million-billion gallons of water?--ThePupil (talk) 02:42, 4 August 2021 (UTC)
- No, since km is a unit of length and gallons is a unit of volume. --OuroborosCobra (talk) 03:20, 4 August 2021 (UTC)
- I recall reading that if all the water in the atmosphere were to rain out, it would only be 1 inch/ 2cm deep on average. This is consistent with atmospheric pressure being 14.7 psi, and water being about 0.25% of that. Abductive (reasoning) 03:51, 4 August 2021 (UTC)
- Ah, I found a USGS website for schoolchildren that says exactly that. Abductive (reasoning) 03:54, 4 August 2021 (UTC)
- No, since km is a unit of length and gallons is a unit of volume. --OuroborosCobra (talk) 03:20, 4 August 2021 (UTC)
- According to the given data, there are 194040000 km of water in the atmosphare, right? Does it go together with Wisconsin university's statement that the Earth’s atmosphere contains 37.5 million-billion gallons of water?--ThePupil (talk) 02:42, 4 August 2021 (UTC)
- To the IP user above: 5.15×1018 kg × 0.4% = 2×1016 kg, not 2×1018 kg. I think you used 0.4 rather than 0.4%, resulting in an estimate that's too high by a factor of 100. The section Atmosphere_of_Earth#Density_and_mass gives this number explicitly as 1.27×1016 kg. --Amble (talk) 17:40, 4 August 2021 (UTC)
- Blast, so I did. Which means that my conclusion that "the water in the atmosphere is... about 0.14% of all the water" was too large by the same factor. If there are no other errors, I should have said 0.0014%. "Thanks for the correction", he muttered angrily. --184.144.99.72 (talk) 21:39, 5 August 2021 (UTC)
1 km³ converts to about 264,000,000,000 US gallons. Therefore "37.5 million-billion gallons", i.e. 37,500,000,000,000,000,000 US gallons, converts to only about 142,000 km³. If the figures in Wikipedia are anywhere near correct, whoever wrote that item at the U of Wisc has gotten it wrong by several orders of magnitude. --184.144.99.72 (talk) 04:20, 4 August 2021 (UTC)
- The USGS website above says that there is 12,900 km3 of water in the atmosphere. So they're only wrong by a bit over 1 order of magnitude. Abductive (reasoning) 07:54, 4 August 2021 (UTC)
The OP linked to the source [7], which says that the water in the atmosphere is "0.001 percent of the total Earth's water volume". That's 0.001% of the water on Earth, not 0.001% of the mass of the atmosphere. So the linked source already gives a direct answer to OP's question. --Amble (talk) 17:42, 4 August 2021 (UTC)
Dimensions
- File:Escher Waterfall.jpg modified per WP:NFCC #9, copyrighted images may only appear in the article namespace. If you wish to view the image to understand the discussion, click the link --Jayron32 13:45, 4 August 2021 (UTC)
The Dutch artist M. C. Escher produced drawings that contain (in many cases) visual paradoxes. For example, "Waterfall" depicts water running downhill in a continuous loop. This is a representation in two dimensions of something that could not be constructed in three dimensions.
Is it possible to construct an object in three dimensions that is a representation of an object that could not be constructed in four dimensions? Ionlywanttoknow (talk) 10:43, 4 August 2021 (UTC)
- The fourth dimension is time. ←Baseball Bugs What's up, Doc? carrots→ 12:19, 4 August 2021 (UTC)
- The question obviously refers to a hypothetical universe with a macroscopic fourth spatial dimension. (And your unhelpful snark means that I have to resolve an edit conflict, so thanks for that.) TenOfAllTrades(talk) 12:43, 4 August 2021 (UTC)
- There's nothing "obviously" about it to me. Though I'm "obviously" a lot dumber than you are. ←Baseball Bugs What's up, Doc? carrots→ 12:48, 4 August 2021 (UTC)
- Time is already implied in the question as posed, which speaks of "water running".
- If someone handed you a photograph of a sphere and asked you to construct a three-dimensional object from it, would you hand the picture back and say "Done! It's a two-dimensional object persisting in time!"? (At least, would you do so without knowing you were being a smartass?) TenOfAllTrades(talk) 13:28, 4 August 2021 (UTC)
- No, I'd construct a sphere. If they wanted a depiction of a four-dimensional sphere, I'd represent it by several spheres, each with a nearby clock showing a different time. ←Baseball Bugs What's up, Doc? carrots→ 14:01, 4 August 2021 (UTC)
- That's only if we're dealing with "three spatial dimensions and one time dimension". We live in that now, it's called Minkowski spacetime, and it is NOT the same thing as "four spatial dimensions", which is something different entirely. We cannot directly observe four spatial dimensions to understand what a 4-sphere would look like, but we can visualize what the 3-dimensional projection of a 4-sphere would look like, in the same way that you can project the shadow of a 3-dimensional sphere onto a 2-D surface, you can project the 3-dimensional "shadow" of a 4-sphere into 3 dimensions. here are a plethora of videos that show you how that works. --Jayron32 18:11, 6 August 2021 (UTC)
- No, I'd construct a sphere. If they wanted a depiction of a four-dimensional sphere, I'd represent it by several spheres, each with a nearby clock showing a different time. ←Baseball Bugs What's up, Doc? carrots→ 14:01, 4 August 2021 (UTC)
- There's nothing "obviously" about it to me. Though I'm "obviously" a lot dumber than you are. ←Baseball Bugs What's up, Doc? carrots→ 12:48, 4 August 2021 (UTC)
- The question obviously refers to a hypothetical universe with a macroscopic fourth spatial dimension. (And your unhelpful snark means that I have to resolve an edit conflict, so thanks for that.) TenOfAllTrades(talk) 12:43, 4 August 2021 (UTC)
- (I've added an image of Escher's Waterfall for reference.)
- It's an interesting question that's got a number of possible answers, depending on exactly what you choose the question to mean.
- A drawing is a notional projection of a three-dimensional structure onto a two-dimensional plane. So one version of your question might be, can you create a three-dimensional figure that represents an implausible 4-D structure? I strongly suspect the answer is 'yes', but you might refer this question to the Mathematics reference desk to address some of the more technical aspects.
- Of course, part of the implausibility lies in the apparent perpetual motion of the water--the apparent defiance of common-sense laws of physics. Addressing the question from that angle means considering how one might generalize our existing physics to a fourth spatial dimension; we can't break the rules in our hypothetical universe if we don't establish what they are to begin with.
- But then there's the third aspect of the question, which is that a lower-dimensional representation or projection necessarily sacrifices information about the higher-dimensional structure. A two-dimensional portrait, no matter how detailed, doesn't display the back of the subject's head. Escher's lithograph seems paradoxical because our brains fill in a presumed structure and orientation and connectivity for the parts of the scene. Escher's Waterfall is an image of an entirely possible, constructible, three-dimensional structure--it just isn't put together the way that you thought it was: YouTube link. TenOfAllTrades(talk) 12:35, 4 August 2021 (UTC)
- Yes, we learn in calculus III, that the surface of n dimension is the n-1 dimension. So the surface of a cube, is a plane. The surface of an object in 4D, is a 3D object. The cube is therefore the surface of whatever 4D objects are called. 67.165.185.178 (talk) 12:54, 4 August 2021 (UTC).
- Sort of. There are many perspectives on the surface of a 4-cube (aka a Tesseract), and some of them do indeed look rather cubish. But by changing the angles by which one observes the 4D object, you can get a variety of rather un-cube-like looking things. While it is true that the surface of a 4-D object is a 3-D object, it's far too simplified to say that the surface of a tesseract is a cube. --Jayron32 18:16, 6 August 2021 (UTC)
- The reason the Escher drawing "works" is despite knowing we're looking at an impossible three-dimensional object, our minds insist on interpreting it as a 3-D object anyway. That's because our brains are very, very good at visualizing things in 3 dimensions. That's in large part due to the fact we live in a three-spacial-dimensional world.
- We do not live in a four-dimensional world and thus we are very, very bad at visualizing four-dimensional objects. The trick becomes getting the mind visualize the fourth spacial dimension in the first place. Yes, we can create a three-dimensional figure that represents an impossible 4-D structure, it just won't look like anything. It's like being told a joke in a language you don't understand. DB1729 (talk) 13:11, 4 August 2021 (UTC)
- To clarify more on what DB1729 is saying, the problem is not one of geometry or physics, it is one of psychology and neuroscience. The illusion of the third dimension is solely a product of the human brain interpreting the series of lines and shading in a certain way, Escher's drawings break your brain, they don't break geometry. It is still just a 2-D series of lines and shades of grey and whatnot, there is no "3Dness" to it except in the way your brain tries to make it so. It is an Optical illusion, caused by an unconscious inference according structuralist psychology; there is also Gestalt psychology, which would have different frameworks for understanding such illusions. Regardless, it's still not a geometry issue, it's a brain issue. --Jayron32 13:51, 4 August 2021 (UTC)
- How about a Klein bottle? It's doesn't really intersect itself, but the best we can do in 3D is have the handle intersect the side where it passes through. DMacks (talk) 18:17, 4 August 2021 (UTC)
- The question asked for a 3D representation of an impossible 4D object. A truly non-intersecting Klein bottle can be constructed in four dimensions, so it is not impossible. As explained above by DB1729 and Jayron32, the illusion of 3D impossible objects depends on the human visual system interpreting 2D images as representing 3D objects. We as humans have no system on board for interpreting a 3D shape as representing a 4D object, so I agree the answer to the question is, "no, it is not possible". --Lambiam 20:42, 4 August 2021 (UTC)
- A 3-D hologram of an apple falling out of a tree. The apple never hits the ground. In 4-D, it would.195.50.139.86 (talk) 06:38, 5 August 2021 (UTC)alien
August 5
angled eyepiece binoculars
There are some very expensive binoculars[8] with angled eyepieces, nice for stargazing without having to tilt your neck so uncomfortably. That one is extreme as I've seen some other ones in the $1000 range. But is there some reason I don't see them at more normal consumer prices, say $100 or so? I have a pair of decent yet affordable 7x50 binoculars with straight eyepieces and am wondering whether angled has to add a lot to the cost. Thanks. 2601:648:8202:350:0:0:0:2B99 (talk) 22:53, 5 August 2021 (UTC)
- It's pretty common in spotting scopes, but I've not seen anything smaller than observation or astronomical binoculars that require tripods with angled eyepieces. --jpgordon𝄢𝄆𝄐𝄇 04:26, 6 August 2021 (UTC)
- Right, but even astronomical binoculars don't have them, except for quite expensive ones. So I am wondering whether the feature was inherently expensive. 2602:24A:DE47:BA60:8FCB:EA4E:7FBD:4814 (talk) 20:13, 6 August 2021 (UTC)
- If you can put one on a $100 spotting scope, not inherently expensive. --jpgordon𝄢𝄆𝄐𝄇 21:32, 6 August 2021 (UTC)
- Oh, one discussion I read said it's a focal length issue. --jpgordon𝄢𝄆𝄐𝄇 21:38, 6 August 2021 (UTC)
- Fair enough, thing is I can't find anything like this (price-wise) with angled eyepieces. Those are 20x80mm so long focal length, big, etc. Same shop has a 70mm pair with angled eyepices but that is $1000+. Oh well, I'm too far from any good dark skies these days to worry about this. Maybe I'll get a folding lawn chair if I start using my 7x50mm more, to make it easier to look straight up. 2602:24A:DE47:BA60:8FCB:EA4E:7FBD:4814 (talk) 23:58, 6 August 2021 (UTC)
- One expedient is to mount a large flat mirror at an (adjustable) angle in front of you thus: <∘)----↑/, and point the binoculars at that. Ideally it should be front-silvered, but you might find you can tolerate the fainter doubled reflection from a conventional back-silvered mirror.
- It might also be possible to firmly mount such a mirror actually on the binoculars, just in front of the objective lenses, but I've never seen that actually done. {The poster formerly known as 87.81.230.195} 2.122.62.68 (talk) 22:12, 7 August 2021 (UTC)
- The principal issue with such a strategy is that you will end up sacrificing field of view and (possibly) brightness. Inserting a mirror between the eyepiece and the viewer will almost certainly move the user's eye back past the maximum eye relief distance of the binocs; they will be left 'peeping through a keyhole' from a distance.
- A minor additional irritation with such an approach is that inserting a single mirror will invert the image. Users of various flavors of astronomical telescopes will be used to having their images inverted in various ways and may not be bothered, but people who are used to the upright images of binoculars or spotting scopes may be discomfited by the change. TenOfAllTrades(talk) 12:29, 8 August 2021 (UTC)
- The mirror is placed in front of the binoculars (see Objective lens), not between the oculars (eye lenses) and the eye: sorry my artwork wasn't up to making this clear. As you say, this inverts the image, but anyone using or intending to use most astronomical instruments will have to get used to this anyway. {The poster formerly known as 87.81.230.195} 2.122.62.68 (talk) 02:45, 9 August 2021 (UTC)
- Fair enough, thing is I can't find anything like this (price-wise) with angled eyepieces. Those are 20x80mm so long focal length, big, etc. Same shop has a 70mm pair with angled eyepices but that is $1000+. Oh well, I'm too far from any good dark skies these days to worry about this. Maybe I'll get a folding lawn chair if I start using my 7x50mm more, to make it easier to look straight up. 2602:24A:DE47:BA60:8FCB:EA4E:7FBD:4814 (talk) 23:58, 6 August 2021 (UTC)
- Right, but even astronomical binoculars don't have them, except for quite expensive ones. So I am wondering whether the feature was inherently expensive. 2602:24A:DE47:BA60:8FCB:EA4E:7FBD:4814 (talk) 20:13, 6 August 2021 (UTC)
August 7
What is the relation between the Atlantic Meridional Overturning Circulation and the North Atlantic Current? Neither article refers to the other, but they seem to be closely related phenomena. --Lambiam 20:03, 7 August 2021 (UTC)
- Those articles don't even have a mutual "see also" entry. It looks to me as though there would be a case for merging the articles, but I know nothing about the subject and suggest you raise it on the respective talk pages.--Shantavira|feed me 11:02, 8 August 2021 (UTC)
- I have left a request for assistance at Wikipedia talk:WikiProject Meteorology. Alansplodge (talk) 11:48, 8 August 2021 (UTC)
August 9
Why does a laptop attracts red ants not black ants?
From here, why does a laptop attracts red ants not black ants? I didn't find any useful information here I too faced same problem with that red ants. Rizosome (talk) 14:46, 9 August 2021 (UTC)
- That link does not say that red ants are particularly attracted to laptops NOR does it say that black ants are not attracted to them. It is just one person saying that their one laptop had been infested by red ants. It should be noted that there are thousands of different ant species, and some are red and some are black and without knowing which we are talking about, it would be difficult to make any useful statements about why one particular species might infest one particular lap top. --Jayron32 15:16, 9 August 2021 (UTC)
- I studied ants at one point. I found that the red ants ate more than the black ants. I could never determine why for sure, but I hypothesized that my experiment had more red ants than black ants. ←Baseball Bugs What's up, Doc? carrots→ 16:03, 9 August 2021 (UTC)
Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination — Kentucky, May–June 2021
Can someone please help me to understand this article in layman's terms?[9] It says that unvaccinated COVID survivors are twice as likely to get reinfected than COVID survivors who get vaccinated. But what does "twice as likely" actually mean? If, for example, the reinfection rate of the former is 93% and 96% for the latter, isn't that "twice as likely"? Is it possible to sus out the actual reinfection rates from this article? A Quest For Knowledge (talk) 20:04, 9 August 2021 (UTC)